The circuit breaker, which is mainly mounted in the transmission end or receiving end of a power transmission line, not only opens or closes normal current when there is no break down in the transmission system, protects the system and many power devices (or loads) by breaking the break-down current when a break down like short-circuit occurs.
These circuit breaker is classified a vacuum circuit breaker (VCB), oil circuit breaker (OCB), and gas circuit breaker (GCB), etc, according to extinguishing/insulating media.
When the breaker isolates break-down current, arc that occurs between electric contacts should be extinguished. The gas circuit breaker is classified puffer type, rotating arc type, thermal expansion type, hybrid extinction type, etc, according to types of extinguishing the arc.
FIG. 1 and FIG. 2 depict a puffer type gas circuit breaker as an example.
The puffer type gas circuit breaker uses SF6 gas (hereafter extinction gases) as extinction/isolation media, and is mainly used for an ultra-high circuit breaker (commonly more than 72.5 KV).
As depicted in FIG. 1 and FIG. 2, the puffer type gas breaker is composed of a breaking part (10), and an actuator (50) for actuating the breaking part (10).
The breaking part (10) is composed of a fixed part and moving part, in which a container (2) stored with SF6 gas is installed. In the breaking part (10), the fixed part includes a fixed arc contacting part (11) and fixed main contacting part (12), and furthermore includes an isolation cylinder (13), fixed piston (14), a holding part (15) and a holding insulator (16), etc.
In the breaking part (10), the moving part includes a moving arc contactor (21), a moving main contactor (22), an insulation nozzle (23), a puffer cylinder (24), and an insulation actuating rod (25).
To the insulation actuating rod (25), an acting rod of the actuator (50) is connected. And to the rod (25), the moving arc contactor (21), the moving main contactor (22), the isolation nozzle (23), and the puffer cylinder (24) are connected as a single body.
Therefore, if the actuator (50) is actuated, the insulation actuating rod (25) moves by the acting rod (51). Then, according to movement of the insulation actuating rod (25), the moving arc contactor (21), the moving main contactor (22), the insulation nozzle (23), and the puffer cylinder (24) moves as a single body, and performs a closing pole action (inserting current) and a opening pole action (cutting off current).
In the concrete, in the steady state, closing state is maintained and steady state current flows.
When a break down occurs in a power transmission system and break-down current, which is many times of normal current (for example, about 10 times), flows, the actuator (50) acts by the break-down current. Then, as depicted in FIG. 2, the acting rod (51) is pulled by the actuator (50), and the acting rod (51) pulls the insulating acting rod (25). Therefore, the moving arc contactor (21) is separated from the fixed arc contactor (11), and the moving main contactor (22) is separated form the fixed main contactor (12).
Concurrently, the puffer cylinder (24) compresses the extinguishing gas in the puffer cylinder (24) by being pulled against the direction of the fixed cylinder (14). The compressed extinguishing gas passes through an inhaling hole (17) and a fluid drain (18), is spouted to the arrow direction in FIG. 2, and promptly extinguishes arc plasma that occurs between the fixed arc contactor and the moving arc contactor (21), then the current is cut off (open pole state).
Like this, for cutting off break-down current and recovering isolation between poles promptly, for the circuit breaker, opening action should be performed on high speed. But as arc plasma is formed, just by separating gap of the opening poles, arc extinction is not performed completely. So, extinction gas should be ejected as described above. Therefore, the actuator (50) is responsible to force for compressing extinction gas, that is, the force for actuating the puffer cylinder against the fixed cylinder (14).
That is, in order to increase actuation power much more to speed up opening pole speed, the actuator (50) needs much more force and speed. For example, a circuit breaker for high/ultra high voltage (commonly more than 365 KV) has stroke length of about 250 mm, needs so big power and speed that it can complete the operation such a little time as 45 ms.
Presently, as a passive element like high/ultra high voltage circuit breaker, mostly oil-pressure actuator or air-pressure actuator is used. But, these actuators are so high that the price of them is about ⅓ of the total price of a circuit breaker. And, this oil-pressure or air-pressure actuator has concern of leaking acting fluid according to temperature change of surroundings. And, as they have a lot of components, the actuator can not operate even if just one of the components is out of order.
Therefore, researches for developing an actuator that can replace the oil-pressure or air-pressure actuator are performed frequently. As results of the research, a spring actuator (spiral spring), motor drive (a system using a motor to convert rotating movement to linear movement), and Permanent magnetic Actuator (PMA) are used typically. As the spring actuator is a system that compresses the spring and gains power by releasing the compressed power, the price of manufacturing is low, but the actuator has a shortcoming that reliability for operation state is low because the elasticity of spring is uneven. For this reason, not only it is not applicable to high voltage or ultra high voltage that should eject extinction gas, but possibility of failure is very high if it is applied.
Even though the motor drive has low manufacturing cost compared to air-pressure or oil-pressure actuator, it is still very high. And it can not make big power, so it can be used for low voltage but can not be used as high voltage or ultra high voltage.
In the PMA, an actuator is driven by electromagnetic force from magnetic force coming from a permanent magnet and electric field generated from a coil. Therefore as it has a very simple structure, has good efficiency for actuation, and can expect a stable and even operation, recently, it is used popularly for actuators for low voltage. But, as the PMA actuator an actuator is driven by electromagnetic force from magnetic force coming from a permanent magnet and electric field generated from a coil, not only a path for flowing magnetic field should be installed by a magnetic material, the acting actuator should be made by a magnetic material. So, when the actuator needs much more force according to increment of cutting off capacity, much magnetic field should be generated, as the magnetic material should be bigger in order not to be magnetic saturation and flow, the size of actuator would be bigger. And since magnetic field density is in inverse proportional to square of gap length, it has limitation to be applied to high or ultra high voltage actuator that has big contact length.
For example, when PMA is applied to an actuator for low voltage that has stroke length of about 20 mm, since the optimal size of the model (length ?width ?depth) is 200×250×100 mm, its weight will be more than 10 Kg. Therefore, when the PMA is used in ultra-high voltage, the size should be much bigger, its weight will be much heavier than that of oil-pressure or air-pressure actuator, and manufacturing cost is increased. For this reason, until now, PMA is not a measure for a high and ultra high voltage actuator.
By solving the problems in conventional actuators, a new actuator, named as EMFA (Electro-Magnetic Force Driving Actuator), having the actuator have small size and weight and maximize operation speed and force, is introduced on the Korea patent application of 10-2005-11263 that was applied by the inventor of this application.
The EMFA includes an inner cylinder and outer cylinder made of magnetic material, inner and outer magnetic field generation element (e.g. permanent magnet) is allocated between the inner and outer cylinder, a coil and a movable body made of non-magnetic material that operates with the coil is allocated between the inner and outer magnetic field generation elements. The EMFA is a new type of actuator that when current is applied to the coil, by electromagnetic repulsion force due to current density of the coil and the magnetic field due to the inner and outer magnetic field generation elements, the coil and actuator move linearly according to axis direction between the inner magnetic field generation element and the outer magnetic field generation element.
As the coil moves as a moving element, the EMFA can maximize actuation forces and speed even though it has small size and weight, increase stroke length of the moving element. Therefore, the actuator using electromagnetic force, not only shows prominent performance in a passive element that needs big actuation force, high speed, and long stroke length like high or ultra high voltage circuit breaker for transmission, to which PMA can not be applied, but can be applied extensively to the passive element like low-voltage circuit breaker.
But, in the EMFA, as the coil is located inside of outer cylinder enclosed from outside, it is not easy to wire for providing current for the coil. And, since allocated wire moves to the direction of axis according to linear movement of the coil, even though the wire is connected, as the speed of the coil is fast, so the wire is experienced with fatigue due to compression and stretching and worried about disconnection of the wire.
And, in the EMFA, as the moving element is located between hollowed inner cylinder and outer cylinder, in order to connect it to outer acting elements, not only a moving axis or a connecting axis should be extended from the moving element, extended length should be long enough to secure the stroke length of the moving element. For this reason, as total height of the actuator, that is, the length of the actuator should be long, be used many ones, or the one that has large radius, the actuator would be heavier.
And, as the coil and the moving element simply are located between the inner and outer magnetic field generation elements without any guiding device, when the coil and the moving element move to axis direction, they make friction with the inner and outer magnetic field generation elements, and due to that, as the actuation force is lost or movement is not good, new consideration is necessary for stable driving of the actuator.
And, in the EMFA, the inner and outer magnetic field generation elements and subordinate magnetic field generation element should be fabricated in cylindrical form. But, in case that the magnetic field generation element is made of a permanent magnet, since it is not easy to be made in a single cylindrical form, there is a difficulty that after actually many parts are made along with direction of cylinder, the several parts should be allocated inside of a casing.
Meanwhile, as described before, not only the actuator should have high acting speed and force, but sometimes have big holding force.
One of passive elements that need big holding power in addition to high acting speed and force is Vacuum Circuit Breaker (VCB).
In FIG. 3, VCR that needs big holding force is depicted.
As depicted in FIG. 3, VCB is divided largely into a contacting part (10z) and actuation part (20z). In the actuation part (20z), conventional PMA (21z) is depicted as an example. The PMA (21z) is located for a moving part (24z), which is composed of magnetic material, to be able to move forward and backward in the longitudinal direction in the path formed in the middle of fixed iron core, in the middle part of the path, a permanent magnet (25z) is located, a closing side coil (26z) and opening side coil (27z) are located in the upper side and lower side of the permanent magnet. The moving part (24z) is connected to the contacting part (10z) by means of link element, etc.
And, in the contacting part (10z), a fixed contacting part (12z) and a moving contacting part (13z) are prepared inside of a insulator that maintains vacuum. The moving contacting part (13z) is responsible for force to drive a link element (30z).
Like FIG. 3, when the moving part (24z) is in the upper side in the figure, the moving contactor (13z) is separated from the fixed contactor (12z), and maintains open pole state (current is cut off). At this time, arc plasma at the contacting part is extinguished by vacuum of insulation material. At this state, when current is inputted in the input coil, the moving part (24z) moves to lower direction of the figure by the magnetic field induced from the input coil and the magnetic field from permanent magnet (25z), and the moving contactor (13z) contacts the fixed contactor (12z) and makes closed pole state (current flowing state, or input state). At closed pole state, in order for the fixed contactor (12z) and the moving contactor (13z) flow current well like a conductor, two contactors should be pressed by powerful force. The force that contacts two contactors (12z) (13z), which is called as the contact force, is responsible for the actuator (20z). Therefore, the actuator should provide enough energy to maintain continuously contacted state with powerful pressure. As such, the energy that the actuator should have is called as holding force. Ordinarily, the holding power of the actuator should be 20% greater than the contacting pressure in order that the contactors don't break away when radical shock from outside such as earthquake is transmitted.
In the point of holding force, in the EMFA that is disclosed in Korea patent application 2005-11263, the actuator is maintained to the moving side state (open state or closed state when applied to the actuator) by the force of magnetic field from magnetic field generation element. The EMFA, as described above, is able to maximize stroke force, stroke speed, and stroke length, and has many merits of having superior performance to PMA. But, holding force that holds the moving part at a moved state is not enough, it is not easily applicable to VCB as it is. For this reason, as a passive element that needs huge holding force should employ a holding force increment means like a double-power apparatus, structure of it is complicated and cost becomes high.